contribute to very peculiar properties [14–22] such as Dirac spectrum of low-lying
quasiparticles [14], large mean-free-path [15], and high electron mobility [23,
24]. Graphene can be synthesized by various means such as exfoliation and
cleavage [15, 25, 26], chemical vapor deposition (CVD) [27–31] and chemical
method [32–35]. The nature of graphene is reported to be a gapless semiconductor
evident from the Dirac energy dispersion and its density vanishes linearly while
approaching the Fermi energy. In fact it acts as a bridging material between semiconductors and metals with a finite density of electronic states at the Fermi energy
level. The gap between the adjacent graphene layers can be opened by chemical
modifications [36, 37] or lateral confinement [38–40] and this results in pushing the
layers apart. During composite fabrication elastomer chains get entrapped in these
gaps and bonding occurs thus reinforcing the matrix.
Nanoclay Figure 1b illustrates the structure of nanoclay with individual platelet
thickness 1 nm and surface dimensions 300–600 nm. These dimensions enhance its
aspect ratio. Examples of nanoclays used in rubber reinforcement include montmorillonite, bentonite, kaolinite, illite, chlorite, smectite etc. Naturally occurring
montmorillonite is hydrophilic and so it is of great difficulty to fill organophilic
polymers with such clays. In this situation modification of nanoclays with
organophilic groups has importance as this process maintains enough rubber-filler
compatibility. The surface compatibilization is also known as intercalation and it is
possible for the macromolecular chains to get in between the intercalated clay
platelets. Sometimes complete delamination of the layers can happen and it is
referred to as exfoliation. This is the ideal situation for maximum rubber reinforcement. The clay composites have many applications such as fabrication of impermeable membranes, tyre inner tubes, textile materials etc. The properties such as
good hardness, scratch resistance and flexibility make montmorillonite (chemically
(Na, Ca) (Al, Mg) 6(SiO 10 ) 3 (OH) 6-nH 2 O or hydrated sodium calcium aluminum
magnesium silicate hydroxide) the most used clay in textile coating [41].
3 Characterization of 2D Fillers and its Nanocomposites
There are a lot of characterization techniques for the two dimensional filler particles
as well as for its composites. Since this is not the subject of this chapter, the two
main methods used to investigate such fillers and nanocomposites formation are
mentioned in this section. These are the transmission electron microscopy (TEM)
and X-ray diffraction (XRD) spectroscopy. A typical TEM image obtained for
pristine graphene and nanoclay is shown in Fig. 2. The flake structures of both
fillers are very clear from this figure and this technique offers the most useful one to
confirm the filler synthesis. The graphene film shown in Fig. 2a has a high contrast
and low contamination level. Such image was obtained by dipping the TEM copper
grids into the solution processed by ultrasound assisted exfoliation during graphene
synthesis and by collecting the graphene flakes on the grids. Thereafter a broad
46
K.K. Sadasivuni and Y. Grohens
quasiparticles [14], large mean-free-path [15], and high electron mobility [23,
24]. Graphene can be synthesized by various means such as exfoliation and
cleavage [15, 25, 26], chemical vapor deposition (CVD) [27–31] and chemical
method [32–35]. The nature of graphene is reported to be a gapless semiconductor
evident from the Dirac energy dispersion and its density vanishes linearly while
approaching the Fermi energy. In fact it acts as a bridging material between semiconductors and metals with a finite density of electronic states at the Fermi energy
level. The gap between the adjacent graphene layers can be opened by chemical
modifications [36, 37] or lateral confinement [38–40] and this results in pushing the
layers apart. During composite fabrication elastomer chains get entrapped in these
gaps and bonding occurs thus reinforcing the matrix.
Nanoclay Figure 1b illustrates the structure of nanoclay with individual platelet
thickness 1 nm and surface dimensions 300–600 nm. These dimensions enhance its
aspect ratio. Examples of nanoclays used in rubber reinforcement include montmorillonite, bentonite, kaolinite, illite, chlorite, smectite etc. Naturally occurring
montmorillonite is hydrophilic and so it is of great difficulty to fill organophilic
polymers with such clays. In this situation modification of nanoclays with
organophilic groups has importance as this process maintains enough rubber-filler
compatibility. The surface compatibilization is also known as intercalation and it is
possible for the macromolecular chains to get in between the intercalated clay
platelets. Sometimes complete delamination of the layers can happen and it is
referred to as exfoliation. This is the ideal situation for maximum rubber reinforcement. The clay composites have many applications such as fabrication of impermeable membranes, tyre inner tubes, textile materials etc. The properties such as
good hardness, scratch resistance and flexibility make montmorillonite (chemically
(Na, Ca) (Al, Mg) 6(SiO 10 ) 3 (OH) 6-nH 2 O or hydrated sodium calcium aluminum
magnesium silicate hydroxide) the most used clay in textile coating [41].
3 Characterization of 2D Fillers and its Nanocomposites
There are a lot of characterization techniques for the two dimensional filler particles
as well as for its composites. Since this is not the subject of this chapter, the two
main methods used to investigate such fillers and nanocomposites formation are
mentioned in this section. These are the transmission electron microscopy (TEM)
and X-ray diffraction (XRD) spectroscopy. A typical TEM image obtained for
pristine graphene and nanoclay is shown in Fig. 2. The flake structures of both
fillers are very clear from this figure and this technique offers the most useful one to
confirm the filler synthesis. The graphene film shown in Fig. 2a has a high contrast
and low contamination level. Such image was obtained by dipping the TEM copper
grids into the solution processed by ultrasound assisted exfoliation during graphene
synthesis and by collecting the graphene flakes on the grids. Thereafter a broad
46
K.K. Sadasivuni and Y. Grohens